1. Field of the Invention
This invention relates to an electronic control device for an internal combustion engine which detects a first crank angle position SGTT and a second crank angle position SGTL on the side of advance ignition angle of SGTT, calculates a target ignition timing at every SGTL, and sets the target ignition timing at every SGTL or at every SGTT depending on a condition of the setting.
2. Discussion of Background
Conventionally, the electronic control device of this kind, obtains a crank angle signal from a crank angle sensor provided in an internal combustion engine (hereinafter, simply engine) as shown in FIG. 4 taking an example of a four cylinder engines. A pulse-like electric signal as shown in FIG. 4 is obtained from the crank angle sensor at every half revolution (180.degree.) of a crankshaft. P1 shown in FIG. 4 is a detection point of the first crank angle position SGTT, and P2 provided on the side of advance ignition angle of P1, a detection point of the second crank angle position SGTL. In FIG. 4, P3 designates a top dead center of the engine, and in this example, SGTT is set at 6.degree. before the top dead center, and SGTL, 76.degree. before the top dead center.
Furthermore, the above mentioned electronic control device measures a detection period T1 of SGTL from the crank angle signal, and calculates and sets the target ignition timing at every SGTL by determining an ignition timing optimum in running condition of the engine, based on an intake air quantity obtained from signals of revolution number of the engine calculated by the period T1, and an air-flow sensor.
When the target ignition timing is set on the side of retarded ignition angle of SGTT, abnormal retarded ignition angle or abnormal advance ignition angle may be generated by rapid acceleration or by rapid deceleration of the engine, respectively. To prevent this abnormality, when the target ignition timing is set on the side of retarded ignition angle of SGTT, the target ignition angle may be set by SGTT, and not by SGTL.
FIG. 9A signifies the above-mentioned crank angle signal, and FIG. 9B, an ignition signal. In this example, the target ignition timing is set on the side of advance ignition angle of SGTT, and the ignition is performed when time elapsed from SGTL reaches a setting timing P1 which corresponds with the target ignition timing.
At this occasion, when a detection timing t2 of SGTT is abruptly changed to t2' as shown in FIG. 9C by rapid acceleration, since the successive ignition is performed at the timing of t1, the ignition timing is abnormally retarded, and misfire of the engine may be caused. Accordingly, in the conventional case, when the target ignition timing is set on the side of advance ignition angle of SGTT, and when the rapid acceleration takes place, the ignition is performed at the detection timing t2' detecting SGTT as shown in FIG. 9D, so that the ignition timing is not retarded abnormally.
As the electronic control device of this kind, for instance, "an electronic ignition control device for an internal combustion engine" shown in Japanese Examined Patent Publication No. 51155/1983, or the like is pointed out.
However, when the target ignition timing is set at every SGTL or at every SGTT depending on the setting condition as mentioned above, if a detection error is generated between SGTL and SGTT which are detected by the crank angle sensor, the target ignition timing is deviated.
Accordingly, when adjustment is made by SGTT as a reference, the detection point of SGTL is deviated by an error portion. Therefore when the target ignition timing is set from SGTL, that is, when a timer is set for generating the ignition signal from the detection point of SGTL, the target ignition timing is deviated. Furthermore, when adjustment is made by SGTL as a reference, the detection point of SGTT is deviated by an error portion. Therefore, when the target ignition timing is set from SGTT, that is, when a timer for generating the ignition signal is set from the detection point of SGTT, the target ignition timing is deviated.
Furthermore, if the crank angle sensor is finely worked so that it detects accurately, measurement error between SGTL and SGTT can be dispensed with. However, it becomes an very expensive one.
Furthermore, in the conventional electronic control device of the engine, it is possible to prevent the abnormal retarded ignition angle by rapid acceleration in the case when the target ignition timing is set on the side of advance ignition angle of SGTT. However, as for the abnormal retarded ignition angle by rapid acceleration in the case when the target ignition timing is set on the side of retarded ignition angle of SGTT, no counter measure is provided to prevent the abnormality.
When the ignition is performed at a timing t4 on the side of retarded ignition angle of SGTT, as shown in the crank angle signal and the ignition signal of FIGS. 10A and 10B, respectively, and when the detection timing t3 of SGTT is abruptly changed to t3' by rapid acceleration as shown in FIG. 10C, the successive ignition is performed at the timing of t4 as shown in FIG. 10D, the ignition timing is abnormally retarded and misfire of the engine may be caused.